EP2336024B1 - Rotor bearing structure, rotorcraft carrying said bearing structure and method for avoiding instable coupling of the system eigenmodes - Google Patents

Description

The present invention is in the field of equipment for motorized flying apparatus comprising a bearing structure connected to a rotor head, such as for a propeller plane or a rotorcraft for example. More particularly, the present invention relates vibration damping mechanisms induced by aeroelastic instabilities resulting from a coupling between the vibration modes of the carrier structure and the vibration modes of the rotor. The invention then relates to a support structure provided with such a mechanism and a flying apparatus provided with a supporting structure.

Among the aircraft, there are flying apparatus provided with a rotor linked to a supporting structure, for example an aircraft equipped with a propeller or a rotorcraft provided with a lift rotor or propulsion.

The rotor conventionally comprises a rotor mast integral with a hub, this hub carrying a plurality of radially distributed blades.

Furthermore, the carrier structure has a cell, sometimes called "fuselage" in which are arranged motor means adapted to drive the rotor in rotation. In addition, the carrier structure comprises a rotor mounting structure for attaching the rotor to the cell.

Such a mounting structure usually comprises mechanical transmission means as well as fixing elements of these transmission means to the cell. For example, a mounting structure of a rotorcraft, called "pylon" by those skilled in the French language and "pylon" in the English language, includes a main gearbox and

Fastening elements of this main transmission gearbox to the cell, such as suspension bars for example.

The motorization means of the carrier structure then drive the rotor via the transmission means of the mounting structure.

The carrier structure and the rotor are each subjected to forced excitation inherent to the speed of advance of the aircraft.

The dynamic excitation of the rotor, for example the rotor of levitation and propulsion of a helicopter, results from aerodynamic loads to which this rotor is subjected, these aerodynamic loads decomposing into fixed axes in a coplanar effort exerted in the general plane of the hub of the rotor which is perpendicular to the axis of rotation of the rotor, in an axial force which is exerted along the axis of rotation of the rotor, and in a coplanar moment acting in a plane perpendicular to the axis of rotation of the rotor tangentially to the rotational movement of the rotor hub. The frequencies of such vibrations in fixed axes that is to say related to the cell of the carrier structure, are equal to the product kbΩ where "Ω" designates the speed of rotation of the rotor, "b" the number of blades and " k "a positive integer. The fundamental frequencies correspond to a number "k" equal to unity. These excitations are transmitted from the rotor to the structure by the pylon.

Similarly, the carrier structure is subjected to forced excitation. For example, the tail boom of a helicopter cell can be excited directly by a turbulent airflow from the main lift and propulsion rotor.

Flying devices equipped with a rotor are generally structured to mitigate the consequences of such vibrations.

For this purpose, it is common to equip the rotor or the structure of antivibration systems, sometimes called resonator, to filter the dynamic forces at the most inconvenient frequencies, from a passenger comfort point of view or to avoid the breakage of passengers. an element subjected to this vibratory fatigue. These antivibration systems are then set to one of the harmonics of the rotational speed of the rotor.

In these circumstances, it was proposed that according to the document FR2808256 (EUROCOPTER FRANCE) for example, pendular resonators according to which heavy elements are mounted pendulum on the hub of the rotor head. Such pendular resonators make it possible to oppose the forced vibrations induced by the moving rotor head, acting along the axis and in the plane of the rotor. The necessary stiffness of these pendular resonators for filtering vibrations is provided by the centrifugal force field due to the rotation of the rotor. This rotation animates around articulations the pendular heavy elements of a harmonic movement whose frequency is multiple of the speed of rotation Ω of the rotor. The structure of these pendular resonators allows their easy integration on the rotor head.

However, such pendular resonators are effective for only a given frequency. Such pendular resonators are arranged to equip a rotor head implanted at the top of the carrier structure, the rotor providing lift or propulsion, and do not take into account the specific characteristics of the bearing structure relating in particular to its mass and its excitation frequency.

Indeed, the resonators have the effect of stifling the vibrations by creating an antiresonance at the given frequency of adjustment. As a result, the resonator generates two new resonances (or modes of vibration) whose two respective frequencies are located on both sides of the antiresonance frequency. The frequency range defined by these two modes remains relatively narrow. Nevertheless, the two modes of vibration created by the resonators are not normally troublesome in that the two resonances differ from the given frequency to be processed.

Vibration damping mechanisms are also known for treating the vibrations that result from the forced excitation of the supporting structure. For example, we can refer to the document FR2784350 (EUROCOPTER FRANCE) which describes a damped resonator arranged to be implanted at the tail of the carrier structure to filter given frequencies.

In addition to the forced excitations, another vibratory phenomenon can be at the origin of major problems.

In the aeronautical field in particular, a problem lies in the attenuation of the vibration phenomena induced by the aeroelastic instabilities experienced by an aircraft in flight. For example, such aeroelastic instabilities may result from the coupling between the modes of vibration of the carrier structure and the flow of air moving around it, namely in particular a fixed wing type structure (wing of airplane) or wing rotating (rotorcraft rotor blades or airplane propeller blades). It is then instabilities known to the skilled person under the general term "floating" or "flutter" in the English language.

Other aeroelastic instabilities correspond for example to instabilities known as "whirl flutter" in English designating the coupling of the vibration modes of a rotor equipped with blades or blades with vibration modes of the supporting structure supporting the rotor.

These "flutter" and "whirl flutter" phenomena are characterized by limit cycle vibrations or vibrations divergences that may lead to breakage of mechanical parts or structural elements. It is therefore imperative to take these phenomena into account in the design of the aircraft so as to push the critical speeds (forward speed, rotational speed of the rotor) beyond the limits of the flight envelope.

In particular for the whirl-flutter, the manufacturers avoid that the rotor vibration modes are likely to couple with the vibration modes of the carrier structure, thus ensuring the compatibility of these two sets. For this it is generally sufficient to ensure the placement of eigenfrequencies and respective damping modes of vibration of the different sets.

However, it is difficult to modify a posteriori modal characteristics of the carrier structure or the rotor, if such phenomena occur during the development of the aircraft. In addition, a manufacturer may have to modify an existing aircraft to meet the specific needs of a user, which may impact the behavior of the aircraft vis-à-vis these instabilities.

To solve these phenomena that may appear as explained above, the manufacturer can not use the previously described resonators that can deal with forced excitation, and not couplings. Therefore, the manufacturer often chooses to modify its carrier structure, stiffening for example, such a modification having a financial cost but also an impact in terms of significant mass. In addition, it may be difficult to make the changes in question on an existing device.

The state of the art further includes the documents EP 0250135 , DE 102007025934 , FR 2769396 and FR 2770825 .

The document EP 0250135 has a structure carrying a rotor.

The document DE 102007025934 presents a machine tool provided with a device comprising springs and dampers to suppress given vibrations.

The document FR 2769396 is aimed at a device for reducing the noise in a cabin and not for avoiding a destructive coupling between the vibration modes of a carrier structure and the rotor of the aircraft, this device comprising at least one sensor for measuring the values of a vibratory and / or acoustic parameter representative of a vibratory and / or acoustic effect of at least one noise source, at least one controllable mechanical means capable of creating a force capable of reducing said vibratory and / or acoustic effect, and a control unit, for controlling the mechanical means, as a function of the values measured by the sensor.

The document FR 2770825 is intended to reduce the vibrations present in the cabin of a rotary wing aircraft by means of a resonator arranged in the cabin.

These documents do not then relate to the resolution of a coupling problem of the vibration modes of a carrier structure and vibration modes of a rotor.

The present invention therefore aims to combat the phenomenon of unstable coupling of the vibration modes of the carrier structure and those of the rotor of an aircraft, by simple means, inexpensive, and can be easily implemented on an existing device. The principle is to bring damping to the mode (s) of vibration of the carrier structure being involved in the unstable coupling.

The object of the present invention is to propose a vibration damping mechanism for flying apparatus provided with at least one rotor head, propeller plane or rotorcraft in particular, which makes it possible to optimize the attenuation of the vibrations induced by the movement of the aircraft. rotor in rotation and to which the cell of the carrying structure of the apparatus is subjected. It is more particularly sought by the present invention to provide such a mechanism which satisfies the required requirements of efficiency, simplicity of structure, mass and compactness allowing its easy implementation, even optional, on the flying apparatus, and which provides a satisfactory compromise in view of the constraints and difficulties that have been stated.

The approach of the present invention has been to provide the carrier structure of the apparatus with a vibration absorption mechanism transmitted by the moving rotor head, which takes into account the characteristics of the rotor-structure coupling, it is that is to say not only those of the blades, but also those of the supporting structure, in particular the characteristics relating to the frequencies and the masses of its own modes. To provide this mechanism optimized efficiency while meeting the criteria of the desired compromise, it is chosen a region of implantation of the mechanism in the transmission of the movement of the rotor head to the structure, which is therefore located near the center of the head rotor or elements rigidly connected to the rotor head, without unduly encumbering the environment of this area and / or generate discomfort, or without giving the structure of the mechanism complexity likely to affect its overall size and / or its lightness and / or its obtaining at lower costs. This zone of implantation of the mechanism is more particularly chosen as being a mounting structure commonly included in the flying apparatus, for assembly to the cell of the carrier structure of power transmission means interposed in the chain. transmission power that extends between the motor means and the rotor rotated by these motor means. Such transmission means are subject to vibration from the rotor, and are organized to be assembled to the cell. Such a mounting structure comprises in particular a main power transmission gearbox produced by the drive means for driving the rotor, which has the advantage of being located close to the rotor head and of being connected in an almost rigid at the mast of the rotor. The vibration absorption mechanism is advantageously grouped into an independent member provided with own fixing means on said mounting structure.

Therefore, the invention relates to a structure carrying a rotor of a flying apparatus provided with a cell and a mounting structure adapted to be engaged on the rotor, the mounting structure comprising driven transmission means. by motor means of the supporting structure.

Such a carrier structure is mainly recognizable in that said mounting structure is equipped with a vibration damping mechanism to prevent the coupling of the vibration modes of the carrier structure and the vibration modes of a rotor which would be fixed to the carrier structure, the mechanism associates in particular a resonator comprising a weighing element mounted movably on the mounting structure, with means for damping the mobility of the heavy element which are interposed between said heavy element and said mounting structure, heavy element being a heavy weight element carried by the mounting structure via a first deformable member retaining its mobility.

The resonator equipped with the damping means is therefore fixed closer to the rotor to optimize its efficiency on the vibrations induced by the rotor, and taking into account the modes of vibration of the carrier structure solicited by a forced excitation to prevent the coupling between the vibration modes of the carrier structure and the vibration modes of the rotor. The assembly of the mechanism on the mounting structure is easy and may be optional, the mechanism being adjustable and / or installed according to the results of instability of the aircraft in flight, without structural modification consequence of said structure mounting.

The mechanism then has the effect of damping the vibrations over a wide frequency range, without creating antiresonance unlike a conventional resonator.

The damping provided makes it possible to modify the vibration modes of the support structure equipped with the mechanism, and thus prevents the creation of a destructive coupling between the vibration modes of the rotor and the bearing structure of this rotor.

Furthermore, according to a variant, the mounting structure including a main power transmission gearbox adapted to be engaged with a rotor mast of a rotor, the proposed damping mechanism is preferably mounted on such a main transmission gearbox. power, commonly interposed between the motor means and the rotor. This main power transmission gearbox is also likely to be a secondary gearbox assigned to drive in rotation of any rotor head, such as a tail rotor head.

The main power transmission having a box bottom connected to the cell of the supporting structure, the damping mechanism can be arranged on the bottom of the box, if the elements between the bottom of the box and the rotor head are sufficiently rigid and that this location is sufficiently sensitive to the movements of the rotor head.

According to another variant, the mounting structure including a main power transmission gearbox adapted to be engaged with a rotor mast of a rotor, the mounting structure having at least one suspension bar connecting an upper part of the transmission box. main transmission of power to the cell, the damping mechanism is mounted on the suspension bar.

According to an exemplary embodiment of the resonator that includes the mechanism, the mobility of the heavy element is a unidirectional mobility in an orthogonal plane and / or a plane parallel to the axis of rotation of the rotor. Since the cell is linked to a three-dimensional reference reference frame comprising a longitudinal axis, a transverse axis and a vertical axis, the orthogonal plane is a plane parallel to the plane passing the longitudinal axis and the transverse axis of this cell.

For example and in a simplified but nevertheless satisfactory embodiment, the mobility of the heavy element is allowed at least in a plane orthogonal to the axis of rotation of the rotor and / or pitch around an axis of this plane.

According to one embodiment, the first deformable member consists for example of any one of the members comprising at least one flexible blade, at least one torsion tube or at least one coil spring, or any other similar member providing mobility of the heavy element.

The damping means are indifferently of the electromagnetic type, of the hydraulic type, or of the type with mechanical or elastic deformation such as for example consisting of at least one second elastically deformable member formed from a high loss angle elastomer. All other types of means capable of damping the movement of the heavy element induced by the vibrations supported by the mounting structure of the transmission means are capable of being exploited.

The first deformable member is a means for opposing the vibrations on a first narrow frequency range induced by a forced excitation to which the rotor is subjected, with damping means which are means for opposing the vibrations to the rotor. origin of instability over a second frequency range wider than said first range.

These functions performed by the first deformable member and the damping means have the result of preventing the occurrence of a destructive coupling between the natural frequency of a natural mode of vibration of a carrier structure and the natural frequency of a clean mode of vibration of an aircraft rotor.

In the latter case, it is for example to increase the critical flutter speed ("flutter" in English) so that the aircraft is not solicited by this phenomenon in its entire flight envelope. Therefore, the damping coefficients of the vibration modes must be positively increased. As a result, the increase in the value of the critical speed leads to an increase in the frequency range, vibrations, justifying the need for a wider frequency band for the operation of the resonator with damping means.

The invention also relates and not exclusively to an application to counter the phenomenon called "whirl flutter" in English by the skilled person.

où m_r représente la masse de l'élément pesant, où ω _s représente la fréquence propre donnée du mode de vibration de la structure porteuse à traiter, et où K_r représente la raideur dudit mécanisme.In another aspect, said weighting element having a given mass, said mode of vibration of the carrier structure being associated with a given natural frequency, the stiffness of said mechanism is equal to: $$K_r={{\omega }_s}^{2*}{m}_r$$

where m _r represents the mass of the heavy element, where ω _s represents the given natural frequency of the vibration mode of the carrier structure to be treated, and where K _r represents the stiffness of said mechanism.

It is noted that the stiffness of said mechanism is surprisingly a function of the given natural frequency of the vibration mode of the carrier structure to be treated and not of a natural frequency of this mechanism.

Furthermore, the invention also relates to a flying apparatus provided with a rotor and a supporting structure comprising a cell and a structure for mounting the rotor to the cell. The apparatus is particularly notable in that the mounting structure is a carrier structure according to the invention as previously described to prevent the coupling of the vibration modes of the carrier structure and vibration modes of the rotor.

Finally, the invention relates to a method for preventing the coupling of the vibration modes of a carrier structure of a flying apparatus and the modes of vibration of a rotor, said bearing structure carrying said rotor of a flying apparatus provided with a cell and a mounting structure adapted to be engaged on said rotor, said mounting structure comprising transmission means driven by motor means of the carrier structure.

According to this method, said mounting structure is equipped with a vibration damping mechanism to prevent said coupling, said mechanism associating a resonator comprising a weighing element mounted to move on the mounting structure with means for damping the mobility of the the heavy element which are interposed between said heavy element and said mounting structure, the heavy element of the resonator being a heavy weight element carried by the mounting structure via a first deformable member retaining its mobility.

où $$\begin{array}{c}M=\left[\begin{array}{cc}{m}_s& \\ & m_r\end{array}\right]{}_{}C=\left[\begin{array}{cc}{c}_r& -c_r\\ {-c}_r& c_r\end{array}\right]{}_{}K=\left[\begin{array}{cc}{m}_s{\omega }_s^2+k_r& -k_r\\ -k_r& k_r\end{array}\right]\end{array}$$

avec « q_i » qui représente le mouvement de la structure porteuse déterminé par des méthodes usuelles, « q̇_i » qui représente la dérivée première par rapport au temps du mouvement de la structure porteuse, « q̈_i » qui représente la dérivée seconde par rapport au temps du mouvement de la structure porteuse, « x » qui représente du mouvement de l'élément pesant déterminée par des méthodes usuelles, « ẋ » qui représente la dérivée première par rapport au temps du mouvement de l'élément pesant, « ẍ » qui représente la dérivée seconde par rapport au temps du mouvement de l'élément pesant, la raideur « K_r » dudit mécanisme d'amortissement étant égale au produit de la masse « m_r » dudit mécanisme d'amortissement et de la fréquence propre « ω _s » donnée du mode de vibration à traiter à la puissance deux,Furthermore, it is conceivable to determine the final mass m _r of the damping mechanism, the damping coefficient c _r end of said damper and K _r final stiffness of the damping mechanism using the weight mechanism m _s given the carrier structure and the natural frequency ω _s given the mode of vibration to be treated of the structure by looking for the eigenvalues of the following system for a plurality of values of the damping coefficient c _{r of} said damping mechanism and the mass m _r of this damping mechanism in order to obtain a maximum damping of the vibration modes of the carrier structure coupled to the damping mechanism: $$\begin{array}{c}M\left(\begin{array}{c}{\ddot{q}}_i\\ \ddot{x}\end{array}\right)+\mathrm{VS}\left(\begin{array}{c}{\dot{q}}_i\\ \dot{x}\end{array}\right)+K\left(\begin{array}{c}{q}_i\\ x\end{array}\right)=0,\end{array}$$

or $$\begin{array}{c}M=\left[\begin{array}{cc}{m}_s& \\ & m_r\end{array}\right]{}_{}\mathrm{VS}=\left[\begin{array}{cc}{\mathrm{vs}}_r& -{\mathrm{vs}}_r\\ {-\mathrm{vs}}_r& {\mathrm{vs}}_r\end{array}\right]{}_{}K=\left[\begin{array}{cc}{m}_s{\omega }_s^2+k_r& -k_r\\ -k_r& k_r\end{array}\right]\end{array}$$

with " q _i " which represents the movement of the carrier structure determined by usual methods, " q̇ _i " which represents the first derivative with respect to the time of the motion of the carrier structure, " q̈ _i " which represents the derivative second relative to at the time of the movement of the supporting structure, " x " which represents the movement of the heavy element determined by usual methods, " ẋ " which represents the first derivative with respect to the time of the movement of the heavy element, " ẍ " which represents the second derivative with respect to the time of movement of the heavy element, the stiffness " K _r " of said damping mechanism being equal to the product of the mass " m _r " of said damping mechanism and the natural frequency " ω _s »vibration mode data to be processed at power two,

Selecting the pair of damping coefficient c _r of said final damping mechanism and final mass m _r of the damping mechanism, we obtain a maximum damping of the vibration modes of the support structure coupled to the damping mechanism. We deduce the final stiffness from the final mass by the following equation: K _r = ω _s ² * m _r .

It is noted that the parameters that are applied to realize said damping mechanism are termed "final".

According to one embodiment, a plurality of values of the damping coefficient c _{r of} said mechanism and of the mass m _{r are} simultaneously scanned . This gives a three-dimensional graph showing the damping coefficient c _{r of} said mechanism and the mass m _r of this mechanism as well as the damping coefficient of the vibration mode of the structure determined using said system. The pair of damping coefficient c _r final and final mass m _r said damping mechanism corresponds to the torque generating a damping coefficient of the vibration mode of the maximum structure.

According to a second embodiment, it is possible to set the damping coefficient c _r to a given value, and then the eigenvalues of the preceding system are sought for a plurality of values of the mass m _r of the damping mechanism. Therefore, a first graph is produced showing, on the abscissa, the quotient of this mass m _{r of the} said damping mechanism and the mass m _s given of the said support structure, and the ordinate the damping coefficient of the vibration mode of the structure obtained. via said eigenvalues.

The curve obtained has a maximum representing an optimum in terms of damping contribution.

As a result, determining the mass m of said final _r damping mechanism for which the quotient of that mass m _r said damping mechanism and the mass m _s given to said bearing structure generates a maximum damping of the support structure.

The final stiffness K _{r of} said damping mechanism is then determined, this final stiffness K _r being equal to the product of the final mass m _r and the natural frequency ω _s given of the vibration mode to be processed at the power of two.

Finally, a search is the eigenvalues of the previous system to a plurality of values of the damping coefficient c _r of said damping mechanism, and using the final mass m _r and the final stiffness previously determined. Consequently, a second graph showing the damping coefficient c _{r of} said damping mechanism is plotted on the abscissa and the damping coefficient of the vibration mode of the structure obtained via said eigenvalues is plotted on the ordinate.

The curve obtained has a maximum representing an optimum in terms of damping contribution.

The final damping coefficient is then equal to the damping coefficient of the damping mechanism generating said maximum.

According to a third embodiment, it is possible to fix the mass m _r and the stiffness K _r of the damping mechanism at given values, and then the eigenvalues of the preceding system are sought for a given value. plurality of values of the damping coefficient c _r . Therefore, we make a first graph showing the abscissa damping coefficient c _r said mechanism and the ordinate the damping coefficient of the vibration mode of the structure obtained via said eigenvalues.

The curve obtained has a maximum representing an optimum in terms of damping contribution.

The final damping coefficient is then equal to the damping coefficient of the damping mechanism generating said maximum.

Finally, the eigenvalues of the preceding system are sought by using the value of the final damping coefficient c _{r of} said damping mechanism and by using a plurality of values of the mass m _r . Therefore, a second graph is produced which has the abscissa of the quotient of this mass m _{r of the} said damping mechanism and the mass m _s given of the said support structure and the ordinate the damping coefficient of the vibration mode of the structure obtained. via said eigenvalues.

The curve obtained has a maximum representing an optimum in terms of damping contribution.

As a result, determining the mass m of said final _r damping mechanism for which the quotient of that mass m _r said damping mechanism and the mass m _s given to said bearing structure generates a maximum damping of the support structure.

The final stiffness K _{r of} said damping mechanism is then determined, this stiffness K _r being equal to the product mass m _r final and the natural frequency ω _s given the vibration mode to be processed at power two

An exemplary embodiment of the present invention will be described with reference to the single figure of the attached plate, which schematically shows a flying apparatus provided with a bearing structure incorporating a damping vibration absorbing mechanism according to the present invention.

In the figure, a flying apparatus 30 essentially comprises a carrier structure 40 and a rotor 20.

In the exemplary embodiment illustrated, which represents a rotorcraft, this carrier structure 40 consists in particular of a cell 1 also called "fuselage" on which are embarked equipment of the flying apparatus, the crew and if necessary of the personnel . The cell comprises motor means 2 for rotating the rotor 20.

This rotor 20 comprises a rotor mast 3 engaged with a rotor head 4. This rotor head 4 comprises in particular a hub 5 which carries blades 6 and which is connected to the rotor mast 3 for its rotational drive.

Furthermore, the carrier structure 40 comprises a mounting structure 8 arranged at the top of the cell 1 to carry the rotor 20. This mounting structure comprises transmission means 7 interposed from then in the power transmission chain between the drive means. 2 and the rotor head 4, and more particularly between the motor means 2 and the rotor mast 3.

Such transmission means 7 consist of a main power transmission gearbox 50 which is commonly fitted to the rotorcraft and which is in connection with the rotor mast 3 for driving a rotor head 4, the main transmission gearbox. power 50 being disposed at the top of the cell 1 of the flying apparatus in ground station.

The main transmission box 50 is therefore located within the mounting structure 8, sometimes called a pylon, which is placed above the cell 1.

In the usual way in the field, the mounting structure 8 is equipped with various fastening elements 9 ', 9 "favoring its stability in particular against the forces and vibrations coming from the rotor 20 to which it is subjected.

For example, the mounting structure may comprise suspension bars 9 'connecting an upper portion 50 "of the main power transmission gearbox to the cell 1. In addition, the can bottom 50' is attached to the cell 1 by a fixing element 9 ", of the type sometimes called" barbecue "by the skilled person or the type sometimes referred to as" sarib "by the skilled person.

The flying apparatus 30 incorporates a mechanism 10 for absorbing the vibrations induced in particular by the moving rotor head 4. The implantation of this mechanism 10 is carried out by means of the mounting structure 8 of the transmission means 7 on the apparatus, and in particular by means of the main power transmission gearbox 50. More particularly, the mechanism 10 is arranged on the side wall of the box bottom 50 'of the main gearbox 50. The mechanism 10 is not arranged between the box bottom 50' and the cell. Similarly according to this variant, the mechanism 10 is not related to the suspension bars but is only attached to the main transmission gearbox.

This mechanism 10 associates a resonator 11 and damping means 12 assigned to this resonator 11 to take into account the characteristics of the carrier structure 40, and in particular its own excitation frequency with regard to the absorption of the vibrations induced by the setting in motion of the rotor head 4 during the displacement of the apparatus.

The resonator 11 comprises a mobile weighing element 13, such as a weighing element weighing, which is fixed on the mounting structure 8 by means of a first deformable member 14. Such an assembly of the weighing element 13 confers on it a mobility adapted to oppose the vibrations experienced by the transmission means 7, and more particularly by said mounting structure 8, and induced in particular by the setting in motion of the rotor head 4.

The first deformable member 14 is a member capable of filtering the vibrations induced by the moving rotor head 4 over a first narrow frequency range. The heavy element 13 is for example mounted movably on the mounting structure 8 in flexion, such as by means of a blade or similar flexible member constituting the first deformable member 14. The mobility of the weighing element 13 is authorized in an XY plane orthogonal to the rotation axis A of the rotor 3, or even in pitch around the Y axis of this plane which is transverse to the general extension direction of the fuselage.

The damping means 12 are interposed between the weighing element 13 and the mounting structure 8, on which they are engaged. In the exemplary embodiment illustrated, the damping means 12 are deformable means of the hydraulic type. The damping means 12 are able to accompany the mobile movement of the weight element 13 as a function of the vibrations transmitted to the mounting structure 8 by the rotor 20, in a second frequency range wider than the first frequency range. relative to the opposition to these vibrations that provides the first deformable member 14. An unstable coupling between the mounting structure 8 and the fuselage 1 is then surprisingly avoided, from an enlargement of the band of frequencies on the basis of which the mechanism 10 is able to filter the vibrations coming from the rotor head 4.

Of course, the damping means may be of the electromagnetic type or else and not exclusively of elastic type with use of a large loss angle elastomer. In this way, the resonator is fixed closer to the rotor, on one of the elements of the mounting structure so as to limit the participation of the higher modes of vibration of the carrier structure and to have the maximum efficiency on the responsible modes unstable coupling. The limitation of the rotor center displacement is a condition to avoid the coupling between the rotor and the structure.

Finally, it should be noted that according to an alternative variant to the schematized variant, the mechanism 10 can be arranged on a suspension bar 9 'for example.

Claims (11)

1. Carrier structure (40) for a rotor (20) of a flying machine (30), the carrier structure being provided with an airframe (1) and a mounting structure (8) suitable for engaging on said rotor (20), said mounting structure (8) comprising transmission means driven by engine means (2) of the carrier structure (40),
   characterised in that said mounting structure (8) is fitted with an anti-coupling vibration-damping mechanism (10) for preventing the coupling of the vibration modes of the carrier structure (40) and of the vibration modes of a rotor (20) which would be fastened to said carrier structure (40), and said mechanism (10) associates a resonator (11) comprising a weight element (13) movably mounted on the mounting structure (8) with damping means (12) for damping the movement of the weight element (13) which are interposed between said weight element (13) and said mounting structure (8), the weight element (13) of the resonator (11) being a flapping weight element carried by the mounting structure (8) via a first deformable member (14) for restraining its mobility.
2. Carrier structure according to claim 1,
   characterised in that the mounting structure (8) includes a main gearbox (50) suitable for engaging with a rotor mast (3) for a rotor (20), and the damping mechanism (10) is mounted on said main gearbox (50).
3. Carrier structure according to claim 2,
   characterised in that said main gearbox (50) has a casing bottom (50') connected to said airframe (1), and said damping mechanism (10) is arranged on said casing bottom (50').
4. Carrier structure according to claim 1,
   characterised in that the mounting structure (8) includes a main gearbox (50) suitable for engaging with a rotor mast (3) for a rotor (20), said mounting structure having at least one suspension bar (9') connecting a top portion (50") of said main gearbox (50) to said airframe (1), and said damping mechanism (10) is mounted on said suspension bar (9').
5. Carrier structure according to any one of claims 1 to 4,
   characterised in that the first deformable member (14) is constituted by any one of the members comprising at least one flexible blade, at least one torsion tube, or at least one coil spring.
6. Carrier structure according to any one of claims 1 to 5,
   characterised in that the damping means (12) are equally well of the electromagnetic type, the hydraulic type, or the elastic deformation type.
7. Carrier structure according to any one of claims 1 to 6,
   characterised in that the first deformable member (14) is a means for opposing vibrations in a narrow, first frequency range which are induced by forced excitation to which the rotor (20) is subjected, and in that the damping means (12) are means for opposing vibrations giving rise to instability over a second frequency range that is broader than said first range.
8. Carrier structure according to any one of claims 1 to 7,
   characterised in that said weight element has a given mass, said vibration mode of the carrier structure is associated with a given natural frequency, and the stiffness of said mechanism is equal to: $$K_r={{\omega }_s}^{\mathit{2}}*m_r$$

   

   
   where m_r represents the mass of the weight element, where ω _s represents the given natural frequency of the vibration mode of the carrier structure to be treated, and where K_r represents the stiffness of said mechanism.
9. Flying machine (30) provided with a rotor (20) and with a carrier structure (40) comprising an airframe (1) and a mounting structure (8) for mounting the rotor (20) to said airframe (1),
   characterised in that said mounting structure (8) is according to any one of the preceding claims for preventing the coupling of the vibration modes of said carrier structure (40) and of the vibration modes of said rotor (20).
10. Method for preventing the coupling of the vibration modes of a carrier structure (40) of a flying machine and of the vibration modes of a rotor (20), said carrier structure (40) carrying said rotor (20) of a flying machine (30), the carrier structure being provided with an airframe (1) and a mounting structure (8) suitable for engaging on said rotor (20), said mounting structure (8) comprising transmission means driven by engine means (2) of the carrier structure (40),
    characterised in that said mounting structure (8) is fitted with a vibration-damping mechanism (10) for preventing said coupling, said mechanism (10) associating a resonator (11) comprising a weight element (13) movably mounted on the mounting structure (8) with damping means (12) for damping the mobility of the weight element (13) which are interposed between said weight element (13) and said mounting structure (8), the weight element (13) of the resonator (11) being a flapping weight element carried by the mounting structure (8) via a first deformable member (14) for restraining its mobility.
11. Method according to claim 10,
    characterised in that the final mass (m_r ) of said damping mechanism, the final damping coefficient (c_r ) of said damping mechanism, and the final stiffness (K_r ) of said damping mechanism are determined with the help of the given mass (m_s ) of said carrier structure and the given natural frequency (ω _s ) of the vibration mode to be treated of the structure:

    - by searching for the eigenvalues of the following system for a plurality of values for the damping coefficient (c_r ) of said damping mechanism and for the mass (m_r ) of the damping mechanism: $$M\left(\begin{array}{c}{\ddot{q}}_i\\ \ddot{x}\end{array}\right)+C\left(\begin{array}{c}{\dot{q}}_i\\ \dot{x}\end{array}\right)+K\left(\begin{array}{c}{q}_i\\ x\end{array}\right)=0,$$

    

    
    where $$M=\left[\begin{array}{cc}{m}_s& \\ & m_r\end{array}\right]C=\left[\begin{array}{cc}{c}_r& -c_r\\ -c_r& c_r\end{array}\right]K=\left[\begin{array}{cc}{m}_s{\omega }_s^2& -k_r\\ -k_r& k_r\end{array}\right]$$

    

    in which q_i represents the movement of the carrier structure, q̇_i represents the first derivative with respect to time of the movement of the carrier structure, q̈_i represents the second derivative with respect to time of the movement of the carrier structure, x represents the movement of the weight element, ẋ represents the first derivative with respect to time of the movement of the weight element, ẍ represents the second derivative with respect to time of the movement of the weight element, and the stiffness (K_r ) of said mechanism being equal to the product of the mass (m_r ) of said mechanism and the given natural frequency (ω _s ) of the vibration mode to be treated to the power two; and

    - by selecting the pair comprising the damping coefficient (c_r ) of said damping mechanism and the mass (m_r ) of said damping mechanism that makes it possible to obtain maximum damping of the vibration modes of the carrier structure coupled to the damping mechanism (10).

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